1. Field of the Invention
The present invention relates to a decoding apparatus and a decoding method and, more particularly, to a decoding apparatus and a decoding method of decoding a bit stream of a transmission-storage system of a high-efficiency compressed signal of, e.g., sounds and images.
2. Description of the Prior Art
One conventional example of a decoding apparatus used in high-efficiency coding systems of this sort is shown in a block diagram of FIG. 1. As shown in FIG. 1, this conventional apparatus comprises a sound-image data decomposer 13, a quantized bit count storage 14, a unit frame length calculator 15, and a decoding processor 16. As shown in FIG. 2, the decoding processor 16 includes an arithmetic unit 19. FIG. 3 shows the general structure of a unit frame which forms a compressed bit stream 101 to be decoded. This unit frame follows sound-image data 204 of an immediately preceding unit frame, consists of a synchronous pattern 201 at the head of the frame, frame information 202, a quantized bit count 203, and sound-image data 204, and is followed by a synchronous pattern 201 of the next unit frame. This conventional apparatus will be described below with reference to FIGS. 1 to 3.
Referring to FIG. 1, the compressed bit stream 101 formed by a high-efficiency compressed signal of, e.g., sounds and images is input from an input terminal 17 to the sound-image data decomposer 13, the quantized bit count storage 14, and the unit frame length calculator 15. Upon receiving the compressed bit stream 101, the quantized bit count storage 14 extracts and stores the quantized bit count 203 (see FIG. 3) of the sound data and the image data contained in the unit frame of this compressed bit stream 101. The sound-image data decomposer 13 receives quantized bit count information 102 output from the quantized bit count storage 14 and decomposes the sound data and the image data contained in the input compressed bit stream 101 from the input terminal 17 by referring to the quantized bit count 203 contained in the quantized bit count information 102. The sound-image data decomposer 13 outputs sound-image data 103 as an object of decoding arithmetic processing to the decoding processor 16. In the decoding processor 16, the arithmetic unit 19 shown in FIG. 2 performs decoding arithmetic processing for the sound-image data 103 and outputs a desired sound-image signal 109 from an output terminal 18 to an external device. Meanwhile, when receiving the input compressed bit stream 101 from the input terminal 17, the unit frame length calculator 15 calculates a unit frame length unique to a compression system by referring to the frame information 202 (see FIG. 3) contained in the compressed bit stream 101. The unit frame length calculator 15 outputs unit frame length information 106 to an external synchronous detector.
Accordingly, the decoding method in the above decoding apparatus comprises, as a main procedure, the steps of extracting and holding the quantized bit count of the input bit stream 101, decomposing the sound data and the image data contained in the bit stream 101 by referring to the quantized bit count, and decoding the decomposed sound data and image data to output a desired sound-image signal.
In the conventional decoding apparatus and its decoding method described above, the length of a total value of the quantized bit counts of sound-image data of a normally compressed bit stream is naturally shorter than one frame length. However, if the total value of the quantized bit counts becomes larger than one frame length due to, e.g., an erroneous operation or a low quality of an encoder, unrecoverable noise is produced in decoding processing. This makes it impossible to normally decode the sound-image data of this compressed bit stream.